Three stage graft copolymers and weathering-stable, dull thermoplastic molding materials containing said copolymers and having good low-temperature toughness

ABSTRACT

Graft copolymers obtained by 
     (A) polymerizing 10 to 89 wt % of a mixture consisting essentially of either 
     (a1) from 70 to 99.89 wt % of a C 1  -C 18  -alkyl ester of acrylic acid, 
     (a2) from 0.1 to 10 wt % of a polyfunctional monomer, 
     (a3) from 0 to 29.89 wt % of an ethylenically unsaturated monomer which differs from (a1) and (a2), is copolymerizable therewith and carries no acid group and 
     (a4) from 0.01 to 10 wt % of a copolymerizable monomer containing at least one acid group 
     or 
     (a5) from 49.99 to 99.99 wt % of at least one diene, 
     (a6) from 0 to 50 wt % of a monomer which is copolymerizable therewith and carries no acid group and 
     (a7) from 0.01 to 10 wt % of a copolymerizable monomer containing at least one acid group 
     in the presence of from 1 to 80 wt % of a cross-linked silicone rubber to form a copolymer A, 
     and 
     (B) polymerizing 10 to 89 wt % of a mixture consisting essentially of 
     (b1) from 50 to 99.99 wt % of a styrene compound of the formula (I) ##STR1## where R 1  and R 2  independently of one another are each hydrogen, C 1  -C 8  -alkyl, etc. 
     (b2) from 0 to 50 wt % of a methacrylonitrile, acrylonitrile, methacrylic acid, acrylic acid, maleic anhydride, etc. monomer 
     and 
     (b3) from 0.01 to 20 wt % of a copolymerizable monomer containing at least one basic group 
     in the presence of the graft copolymer (A) and used to prepare thermoplastic molding materials.

This is a divisional of application Ser. No. 08/352,750, filed Dec. 2, 1994, now U.S. Pat. No. 5,585,436.

EXAMPLES

The notched impact strength a_(k) (injection molding temperature/test temperature) (in kj/m²) was determined at test temperatures of 23° C. and -40° C. according to DIN 53453 using standard small bars injection molded at 220°, 250° and 280° C.

The surface quality (dull or glossy) was determined visually by viewing under sunlight at an angle of 45° to the surface of the shaped article.

The stated median particle sizes are the weight average of the particle sizes which were determined by means of an analytical ultracentrifuge according to the method of W. Scholtan and H. Lange, Kolloid-Z. and Z. Polymere 250 (1972), 782-796. The ultracentrifuge measurement gives the integral mass distribution of the particle diameter of a sample. From this it is possible to determine the percentage by weight of particles which have a diameter equal to or smaller than a certain size. The median particle diameter, which is also referred to as the d₅₀ value of the integral mass distribution, is defined as the particle diameter at which 50% by weight of the particles have a diameter smaller than the diameter corresponding to the d₅₀ value. Likewise, 50% by weight of the particles then have a diameter larger than the d₅₀ value.

1. Preparation of the graft copolymers A

1.1 A crosslinked polydimethylsiloxane emulsion (prepared similarly to Example 1 of EP-A 492 376) was used as silicon emulsion A1: solids content (SC): 17.4%; particle diameter 156 nm; viscosity 4.6 mPa.s; pH 7; degree of crosslinking 3%; 0.5% of methacryloyloxypropyl functions.

1.2 Preparation of the 1st shell A2

1.2.1 Initially taken mixture Emulsion A1 (cf. Table 1) and water were heated to 60° C. and potassium persulfate (KPS) was then added.

1.2.2 Feed A mixture of n-butyl acrylate (BA) and the acrylate of tricyclodecenyl alcohol (DCPA) was then added dropwise in the course of 1.5 hours. At the same time, a mixture of water and the sodium salts of a mixture of C₁₃ - and C₁₄ -alkanesulfonic acids (soap) was added dropwise. The emulsion A2 obtained was not isolated.

1.3 Preparation of the 2nd shell

5.1 g of potassium persulfate were added to the emulsion A2 and the monomers from Table 1 (styrene, acrylonitrile and, if required, dimethylaminoethyl acrylate (DMAEA)) were added dropwise in the course of 3 hours. Stirring was continued for 2 hours. Theoretical solids content: 40.0%.

                  TABLE 1     ______________________________________     Preparation of siloxane/acrylate rubbers     (All stated amounts in gram)     Experiment:  1 (Comparison)                              2 (Comparison*)                                          1     ______________________________________     Initially taken mixture     Component A1 1839                    1839     Water        3086                    3086     KPS          4.8                     4.8     Feed     BA           1568                    1552     Methacrylic acid                  --                      16     DCPA         32                      32     Water        212                     212     Soap         8                       8     Feed 2     KPS          5.1                     5.1     Acrylonitrile                  320                     320     Styrene      960                     935     DMAEA        --                      25     Mechanical properties     a.sub.K (220/23)                  26          21          24     a.sub.K (250/23)                  25          19          27     a.sub.K (280/23)                  26          19          25     a.sub.K (280/-40)                  4           1           4     Surface      glossy      dull        dull     ______________________________________      *)According to the prior art EP 450511, Table 1, Example 2.

Experiment 1 and Comparative Experiment 2 had the same amount of comonomers but the latter had no silicone core.

Component B

A solution polymer of styrene and acrylonitrile in the weight ratio of 65:35, having a viscosity number of 80 ml/g (measured at 23° C. in a 0.5% strength by weight dimethylformamide solution) was used.

Preparation of the mixtures

The rubbers (Experiment V1, V2 and 1) were mixed with the component B in a weight ratio of 1:1, the mixture was extruded at 250° C. in a ZSK 30 twin-screw extruder from Werner & Pfleiderer and the extrudate was granulated. Moldings for mechanical testing were produced from the granules at 220°, 250° and 280° C. (Table 1). 

We claim:
 1. A thermoplastic molding material comprising (I) from 1 to 95% by weight of a graft copolymer prepared by (A) polymerizing from 10 to 89% by weight based on the total amount of said graft copolymer of a mixture consisting essentially of either(a1) from 70 to 99.89% by weight of a C₁ -C₁₈ -alkyl ester of acrylic acid, where the alkyl radical is optionally monosubstituted by phenyl or phenoxy, (a2) from 0.1 to 10% by weight of a polyfunctional monomer which is a vinylically unsaturated compound having at least two double bonds, (a3) from 0 to 29.89% by weight of an ethylenically unsaturated monomer which differs from (a1) and (a2), is copolymerizable therewith and carries no acid group or basic group and (a4) from 0.01 to 10% by weight of a copolymerizable monomer containing at least one acid group or at least one basic group or (a5) from 49.99 to 99.99% by weight of at least one diene, (a6) from 0 to 50% by weight of a monomer which is copolymerizable therewith and carries no acid group and (a7) from 0.01 to 10% by weight of a copolymerizable monomer containing at least one acid group or at least one basic groupin the presence of from 1 to 80% by weight of a crosslinked silicone rubber based on the total amount of said graft copolymer to form the copolymer A and (B) polymerizing from 20 to 89% by weight based on the total amount of said graft copolymer of a mixture consisting essentially of (b1) from 50 to 99.99% by weight of a C₁ -C₈ alkyl ester of methacrylic acid or acrylic acid and/or a styrene compound of the formula (I) ##STR2## where R¹ and R² independently of one another are each hydrogen, C₁ -C₈ -alkyl or C₁ -C₄ -alkyl-monosubstituted, C₁ -C₄ -alkyl-disubstituted or C₁ -C₄ -alkyl-trisubstituted phenyl, (b2) from 0 to 50% by weight of a monomer selected from the group consisting of methacrylonitrile, acrylonitrile, methacrylic acid, acrylic acid, maleic anhydride, maleimide N-substituted by C₁ -C₄ -alkyl, vinyl esters of aliphatic C₂ -C₈ -carboxylic acids, acrylamide and vinyl methyl ether and p1 (b3) from 0.01 to 20% by weight of a copolymerizable monomer containing at least one basic group or at least one acid group in the presence of the copolymer (A)with the proviso that when the at least one group of (a4) or (a7) is an acid group, the at least one group of (b4) is a basic group and when the at least one group of (a4) or (a7) is basic group the at least one group of (b4) is an acid group, said thermoplastic molding material further comprising (II) at least one thermoplastic polymer having a glass transition temperature of more than 25° C. as a matrix.
 2. The thermoplastic molding material as defined in claim 1 further comprising additives and assistants.
 3. The thermoplastic molding material as defined claim 1 wherein the at least one group of (a4) or (a7) of the graft copolymer is a basic group, and the at least one group of (b3) of the graft copolymer is an acid group.
 4. A thermoplastic molding material as defined in claim 1 wherein the graft copolymer has a median particle size of from 0.05 to 10 micrometers.
 5. The thermoplastic molding material of claim 4 wherein in the graft copolymer a C₂ -C₄ -alkyl ester of methacrylic or acrylic acid, where the C₂ -C₆ -alkyl moiety is monosubstituted or disubstituted by amino is used as component (a4) and an alpha, beta-unsaturated C₁ -C₆ -carboxylic acid us used as component (b3).
 6. The thermoplastic molding material of claim 1 wherein the at least one group of (a4) or (a7) is an acid group, and the at least one group of (b3) is a basic group.
 7. A molding prepared from the thermoplastic molding material as defined in claim
 1. 